Thermostat And Coolanto Utlet; Crankshaft And Bearings - GMC T Series 1994 Repair Manual

Figure 35— Checking the Valve Seals
5. Cap (21) or rotator (28).
• Compress the valve spring using J 8062 (figure
31), enough so the lower valve stem groove can be
seen clearly.
6. O -ring seal (23) onto the valve stem 's lower
groove, making sure the seal is flat and not twist­
ed.
7. Apply a small amount of grease to the area of the
upper valve stem groove.
8. Assemble the two valve keepers into the upper
groove using the grease to hold them in place.
• Release the compressor tool J 8062, making sure
the valve keepers stay in place.
9. Repeat the preceding steps on the remaining
valves.
L*
Inspect
O-ring seals for leakage (figure 35).
A. Place the suction cup supplied with J 23738-A
over the shield.
B. Connect J 23738-A to the suction , cup and
apply a vacuum.
C. Watch the vacuum pump gage, no air should be
able to leak past the seal.
• If the seal will not hold a vacuum, it may have
been damaged or improperly installed.
D. Repeat the preceding steps on the remaining
valves.
Measure
• Valve spring installed height of each spring as fol­
lows.
1. Use a narrow thin scale. A cutaway scale may be
helpful.
2. From the top of the shim or the spring to the top of
the shield.
3. If this measurement exceeds the amount given in
" Specifications," install valve spring seat shims,
approximately 1.6-mm (1/16-inch) thick, between
the spring and cylinder head. NEVER shim the
spring so as to give an installed height under the
specified amount.
THERMOSTAT AND COOLANT
O UTLET
til
Remove or Disconnect
1. Bolts.
2. Coolant outlet.
3. Gasket.
4. Thermostat.
Inspect
I?
Coolant outlet for cracks.
"► + Install or Connect
1. Thermostat.
2. New gasket.
3. Coolant outlet.
NOTICE: Refer to "Notice" on page 6A3-1.
4. Bolts.
Tighten
• Bolts to 28 N-m (21 lbs. ft.).

CRANKSHAFT AND BEARINGS

Some engines may have rear main bearings that are
0.008 inch wider than standard across the thrust faces.
The crankshaft on these engines can be identified by
" .008"stamped on the rear counterweight.
Clean
Crankshaft with solvent.
— Do not scratch the bearing journals.
— Remove all sludge from the oil passages with
compressed air.
Main bearing inserts.
— Wipe free of oil with a soft cloth.
Inspect
L 1
In general, the lower inserts (except the #1 bearing),
show the greatest wear and distress from fatigue. Upon
inspection, if the lower insert is suitable for reuse, it can
be assumed that the upper insert is also satisfactory. If
the lower insert shows evidence of wear or damage,
both the upper and lower inserts must be replaced.
• Main bearing inserts for scoring or other damage.
• Crankshaft for cracks.
— Use the magnaflux method, if available.
• Crankpins, main bearing journals and thrust sur­
faces for scoring, nicks or damage caused by lack
of lubrication.
Measure
Main bearing and connecting rod journal diameters
(figure 36). Compare with " Specifications."